In recent years, in wireless communication using wireless terminals such as cellular phones, radio devices have been used, which are wireless devices having for example a function of modulating and demodulating radio waves and transmitting and receiving radio waves from an antenna. For such radio devices, a technology is known in which an antenna is shared by different services employing the same frequency band and as a result the antenna cost is reduced. Examples of services that employ the same frequency band include a service that employs both code division multiple access (cdma) 2000 and long term evolution (LTE) and a service that employs just cdma 2000.
FIG. 5 illustrates an example of outgoing signals of radio devices of the background art. In addition, FIG. 6 illustrates an example of incoming signals of the radio devices of the background art. In FIGS. 5 and 6, an example is illustrated in which an antenna 672 is shared by a radio device 600 that provides a service employing both cdma 2000 and LTE and a radio device 700 that provides a service employing just cdma 2000. In FIGS. 5 and 6, to simplify illustration, illustration of the internal structures of the radio devices 600 and 700 has been appropriately omitted.
As illustrated in FIG. 5, a special filter 800 (for example, a constant impedance bandpass filter (CIB)) is used in order to allow the antenna 672 to be shared by the radio device 600 and the radio device 700. The special filter 800 includes hybrid circuits (HYBs) 810 and 816, band pass filters (BPFs) 812 and 814 and a cdma duplexer (DUP) (transmission/reception switcher) 818.
Next, the frequency division filter waveforms of the special filter 800 and a general filter will be described. FIG. 7 illustrates an example of the frequency division filter waveform of the special filter. FIG. 8 illustrates an example of the filter waveform of the general filter.
As illustrated in FIG. 7, an LTE band 320 and a cdma 2000 band 330 are used by a service employing both cdma 2000 and LTE. In addition, a cdma 2000 band 340 is used by a service employing just cdma 2000. As illustrated in FIG. 7, the LTE band 320, the cdma 2000 band 330 and the cdma 2000 band 340 lie within the same frequency band. Accordingly, the special filter 800 has a steep filtering characteristic as indicated by a filter waveform 350 so that the cdma 2000 band 340 may be discriminated from the other bands. By using the special filter 800, it is possible to allow only the cdma 2000 band 340 to pass through the filter. In contrast, as illustrated in FIG. 8, the general filter has a gently sloping filtering characteristic as indicated by a filter waveform 370 and a comparatively wide frequency band 360 is allowed to pass therethrough.
The description will now return to FIG. 5. As illustrated in FIG. 5, the radio device 600 has an ANT-A port 662, an LNA-A port 664, an ANT-B port 666 and an LNA-B port 668. The radio device 600 receives baseband signals from a cdma baseband unit (BBU) 850 and an LTE BBU 900 ((1) in the figure). The radio device 600 subjects the received baseband signals to transmission processing ((2) in the figure) and outputs the signals subjected to the transmission processing to the special filter 800 via the ANT-B port 666 ((3) in the figure). The signals input to the special filter 800 are completely reflected by the HYB 810 and are radiated from the antenna 672 ((4) in the figure).
On the other hand, the radio device 700 has an ANT-A port 762, an LNA-A port 764 and an ANT-B port 766. The radio device 700 receives a baseband signal from a cdma BBU 950 ((1)′ in the figure). The radio device 700 subjects the received baseband signal to transmission processing ((2)′ in the figure) and outputs the signal subjected to the transmission processing to the special filter 800 via the ANT-A port 762 ((3)′ in the figure). The signal input to the special filter 800 passes through the special filter 800 and is radiated from the antenna 672 ((4)′ in the figure).
Next, as illustrated in FIG. 6, a baseband signal received from the antenna 672 is input to the special filter 800 ((1) in the figure), is totally reflected by the HYB 810 and is output from the special filter 800 ((2) in the figure). The baseband signal totally reflected by the HYB 810 is input to the radio device 600 via the ANT-B port 666 and is subjected to digital processing inside the radio device 600 ((3) in the figure). Signals obtained by separating the input signal into cdma and LTE signals by the digital processing are respectively transmitted to the cdma BBU 850 and the LTE BBU 900 ((4) in the figure).
On the other hand, a baseband signal received from the antenna 672 is input to the special filter 800 ((1) in the figure), is totally reflected by the HYB 810 and is output from the special filter 800 ((2) in the figure). The baseband signal totally reflected by the HYB 810 is input to the radio device 600 via the ANT-B port 666 and is output from the radio device 600 to the special filter 800 via the LNA-B port 668 ((3)′ in the figure). The baseband signal input to the special filter 800 is input to the ANT-A port 762 of the radio device 700 via the cdma DUP 818 ((4)′ in the figure). The radio device 700 subjects the input baseband signal to digital processing ((5)′ in the figure) and then transmits the signal to the cdma BBU 950 ((6)′ in the figure).
Thus, in the background art, the radio device 600 and the radio device 700 may share the antenna 672 by using the special filter 800 having a steep filtering characteristic.
An example of the background art is Japanese Laid-open Patent Publication No. 2-022931.